Electrical system for signaling between a floating vessel and a subsea well



ELECTRICAL SYSTEM FOR SIGNALING BETWEEN A FLOATING VESSEL AND A SUBSEA WELL Filed Sept. 9, 1968 5 SheetsSheet 1 INVENTOR. DANIEL SILVERMAN flaw ATTORNEY D. SILVERMAN Feb. 24, 1970 ELEc SYSTEM FOR SIGNALING BETWEEN G VESSEL AND A SUBSEA WELL 5 Sheets-Sheet 2 TRIC A FLOA Filed Sept. 9, 1968 A. C.SOURCE INVENTOR. DAN tEL SILVERMAN 20.1% M

ATTORNEY Feb. 24, 1970 D SILVERMAN 3,497,369

ELECTRICAL SYSTEM FOR SIGNALING BETWEEN A FLOATING VESSEL AND A SUBSEA WELL: Filed Sept. 9. 1968 5 Sheets-Sheet 3 m v a n 7 5 A QE MILTERS FIG. 30

FIG. 3b

5o 46 44 AC. SOURCE FIG. 4

FIG. 5

INVENTOR. DANIEL SILVERMAN ATTORNEY Feb. 24, 1970 SILVERMAN 3,497,869

ELECTRICAL SYSTEM FOR SIGNALING BETWEEN A FLOATING VESSEL AND A SUBSEA WELL Filed Sept. 9 1968 5 Sheets-Sheet 4 Blb' -s2' 60a 62 63 60b w em INVENTOR. .FIG. 7 DANIEL SILVERMAN d M ATTORNEY i Feb. 24, 1970 D. SILVERMAN 3,497,569

ELECTRICAL SYSTEM FOR SIGNXLING BETWEEN A FLOATING VESSEL AND A SUBSEA WELL- Filed Sept. 9 1968 5 Sheets-Sheet 5 Fw L FIG. 9

86 us M p7 323 (I06 [I08 :10

RECTlFlER- A.C.SOURCE FIG. 8 BATTERY INVENTOR. DANIEL SILVERMAN BY 9, M

ATTORNEY US. Cl. 340-4 Claims ABSTRACT OF THE DISCLOSURE In offshore drilling and producing operations, it is frequently necessary to lower pipes, such as riser pipes, from a floating drilling vessel to a subsea well and to signal between the vessel and the subsea well. Electrodes mounted on the sea floor and symmetrically placed with respect to the well, supplied with AC. current, set up a potential field. A plurality of electrodes supported by the riser pipe are immersed in this potential field and send signals to the vessel indicating their individual potentials. The pattern of potentials on the plurality of electrodes indicates the position of the pipe with respect to the well. Modifications are described.

BACKGROUND OF THE INVENTION Field of the invention This invention is concerned with the drilling and production of oil and gas wells in offshore areas. More particularly, it concerns means for indicating the relative position of a subsea well and the drilling or producing apparatus, supported by and lowered from a floating vessel. It includes also the signaling from the vessel to the subsea installation as well as the signaling from the installation to the vessel.

Description of the prior art In the drilling for and production of oil and gas in offshore locations, particularly in deep water, it is necessary to have some means of re-entry of drilling or producing means into the subsea well once they have been removed. In relatively shallow Water, this can be done by the use of divers at the subsea well location observing the apparatus and signaling the operators on the floating vessel from which the drilling means, such as riser pipe, drill pipe, etc., depends. In deep or murky water this is not possible. There are also sonic means using a plurality of stationary pulsed sonic sourses symmetrically placed on the sea floor, cooperating with a receiver mounted on the lower end of the riser pipe. By noting the travel States Patent time of the sonic pulses from each of the separate sources In this invention, an electrode system of specified geometry is mounted on the sea floor in precise geometric relation to the subsea well. The electrodes are powered by a source of monofrequency A.C. current. This sets up a potential field in the sea water between the electrodes which is symmetrical with respect to the well. A symmetrical pattern of electrodes is mounted on the riser pipe or other drilling producing apparatus being lowered from the floating vessel for entry into the well. Each of the electrodes is connected by electrical conductor up the riser pipe to the vessel, where they are connected to voltmeter means to indicate some function of their individual potentials. The potential on each electrode is a function of the part of the potential field in which it is placed. Thus by observing the potentials on each of the plurality of electrodes, the riser pipe can be moved in the proper direction until the electrodes on the riser pipe (and thus the pipe itself) are symmetrically placed with respect to the electrodes on the sea floor, and thus with respect to the subsea well.

In addition, in a preferred embodiment, means are provided on the riser pipe, powered by a source of single frequency AC. on the vessel, for signaling to the electrode system on the sea floor. By this means, Signals, power or commands can be sent from the vessel to the well apparatus on the sea floor, and signals can be sent from the well apparatus to the vessel.

It is, therefore, a principal object of this invention to provide a means for signaling from a first electrical A.C. system on the sea floor to a second electrical means sup ported on an elongated structure hanging from a floating vessel. The signals can be for determining relative position of the two systems, or they can be for transmittal of data. Another object is to provide means for transmitting power and signals from the floating vessel to the electrical system on the sea floor.

These and other objects and details of this invention will be made clear from the following description of the invention taken in conjunction with the attached drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a schematic view of a floating vessel, the dependent structural means and the subsea well;

FIGURE 2a is a vertical view of indications of electrical potential about the well ahead and position of detecting electrodes;

FIGURE 2b illustrates one embodiment of the invention using circular symmetry of the sea floor electrode system, and a triangular pattern of detectors;

FIGURES 3a and 3b indicate alternate means of indicating the potentials on the electrodes;

FIGURES 4, 5 and 7 indicate another embodiment using rectangular symmetry;

FIGURE 6 indicates a system for signaling from the vessel to the well;

FIGURE 8 indicates an alternate detail of the system of FIGURE 6, and

FIGURE 9 indicates an alternate detail of the system of FIGURE 2b.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the figures, and in particular, to FIGURE 1, I show in simplified form a drilling vessel 8 floating on the surface of a body of water or sea 9. This vessel has a central opening 7 or moon pool through which drilling apparatus, such as the riser pipe 20, is lowered from the ship to the sea floor. All such drilling apparatus is well known in the art and form no part of this invention.

The novely of this invention lies in the means by which the position of the lower end of the riser pipe 20 with respect to the casing 10 in the earth under the sea can be determined. These means involve electrode 12 on the sea floor, and electrodes A, B, C, attached to the riser pipe. The electrodes A, B, C are connected by conductors 71 to indicating meters 34 on the ship. All of these features will be described more fully in connection with the other drawings.

In FIGURES 2a and 2b I show an oil well casing placed in a drill hole in the ear.h below the water 9, with its top 10a projecting into the sea water above the sea floor 11. Encircling this casing symmetrically is a circular uninsulated conductor or ring electrode 12 set on insulators 13 so that its plane is close to the level of the top of the casing 10a.

A source of AC. voltage 30 is provided with its output leads connected to a stepdown transformer 35, the low turns Winding 37 of which is connected by leads 15, 17 to points 16 and 18, respectively, on the casing and on the ring electrode. The source 30 is supplied with power from a self-contained power source such as battery 31 connected through switch 32.

Numeral 20 represents a casing, riser pipe, drill pipe, or other elongated structural element that must be positioned in or close to the casing. For convenience this will be designated as a riser pipe or, simply, pipe. This is generally lowered from the drill ship 8 or other structure floating on the surface of the sea 9 until it is just above the sea floor. This invention serves to provide an indication to the operators on the ship, for example, of the position of the pipe 20 in relation to the casing top portion On the lower end of the pipe 20 is a structure or plate of insulating material 2.1, triangular in shape, with three electrodes A, B, C, mounted on the corners of the plate, which is itself fastened to the pipe by conventional means. The radius of the electrode circle is less than the radius of the ring, preferably in the order of /2 the radius of the ring. The radius of the ring is chosen to be comparable to the maximum displacement of the pipe from the casing for which a useable indication of position can be obtained. This could be of the order of 50 or 100 feet or more, depending on the power available from source 30.

The sea water environment in which the casing, ring and plate are placed is electrically conducting. Thus, with an AC. voltage impressed between the casing and ring, current will flow. This is indicated by the radial lines 25 in FIGURE 2a and the curved lines 25a in FIGURE 2b. The resistance of the path from 10 to 12 will be low, and, therefore, the power source feeding it should be of low impedance. This can be done by using a stepdown transformer with high turns winding 39 connected to the power source 30, and the low turns winding 37 connected between casing and ring.

There will be equipotential surfaces indicated by the dashed lines 26a in FIGURE 2b and the circles 26 in FIGURE 20. An electrode placed in the potential field 25 will take up the potential of the equipotential surface 26 passing through its position. Thus, the potentials of the electrodes A, B, C should indicate the precise position of the electrodes in relation to ring 12 and casing 10.

For example, in FIGURE 2a I show in the dashed position, electrode A on equipotential surface 4, B on surface 1 and C on surface 6. When the pipe 20 is centered over the casing 10, the electrodes will all be positioned on the same equipotential surface 26 having a designated potential 3. By observing the potential of each electrode, the pipe 20 is moved in the proper direction to bring the electrode with the highest potential in toward the pipe 20. This will bring its potential down, and raise the potential of the other two. This process is continued until all three potentials are equal. The pipe 20 will then be centered over the casing.

The three electrodes A, B, C are shown in FIGURE 3a connected by leads 71a, 71b, 710, respectively, to three voltmeters 34a, 34b and 34c mounted on the vessel. The second lead 36 to each of the voltmeters goes to a distant electrode 38 in the water. Comparison of the readings of the three voltmeters will give an indication of the position of the pipe 20 with respect to the casing 10. To improve the signal to noise ratio, sharp bandpass filters 73a, 73b, 730 can be used.

It will be clear also, as shown in FIGURE 3b, that the three indicating voltmeters can be connected so as to measure the difierence in potential between adjacent electrodes, rather than the potential of each electrode. This is done by connecting each voltmeter, such as 34a between leads 71a and 710, connected to electrodes A and C, respectively and so on. In the symmetrical position of pipe 20 over casing .10, all three voltmeters should read zero. Of course, there are many other ways in which the three potentials indicated by meters 34 can be indicated and displayed, as is well known in the art. It is possible also to devise a servo system to utilize these potentials and to automtaically position the pipe 20 to its proper position.

There are other configurations of electrodes than the circle 12 and casing 10. In FIGURE 4, I show a pair of parallel linear electrodes 40a, 40b placed on insulators (not shown) like electrodes 12 on insulators 13, and spaced equally on opposite sides of the casing 10. The inner electrode can be the casing 10, or preferably a little larger square conductor 52, with sides parallel to elongated electrodes 40a, 4%. AC. power is again supplied by a stepdown transformer 48 with low turns winding 49 connected by lead 47 to the square 52 (and by 54 to the casing) and by leads and 46 to electrodes 40a and 40b, respectively. As shown in FIGURE '5, two electrodes a 60b are mounted on the ends of an insulator 62. The positions of the electrodes 60a, 6017 are indicated in the potential field of FIGURE 4. The two electrodes 69a, 60b can be connected by leads 63, 64 to voltmeter 66 (as in FIGURE 3b) or two voltmeters can be separately connected to leads 63, 64, respectively, and to a distant electrode as in FIGURE 3a.

As in the case of FIGURES 2a, 212, current will fiow from the square 52 to the electrodes 40a, 40b as indicated in general form by the current lines 56. There will also be equipotential surfaces, the traces of which are indicated by dashed lines 58. The electrodes 60a, 60b will indicate their position by their potential, and thus they can be moved parallel to the line joining them until they are symmetrically placed with respect to the casing 54.

Since the traces 58 of the equipotential planes are essentially straight lines parallel to the electrodes 40, the potential on the electrodes 60 do not indicate the position of the arm 62 perpendicular to its direction. T 0 get this indication of position we need a second pair of electrodes 42a, 42b and a second pair of electrode 61a, 61b, FIGURE 7, mounted on an insulator 62' at right angles to 62. In the interest of clarity and simplicity this has not been shown on FIGURE 4, but would be similar to the circuit elements shown for the electrodes 40a, 40b. Preferably, the frequency of the power source for the electrodes 42 would be different from the frequency of the power source for electrodes 40, so that each of the electrode pairs 60a, 60b and 61a, 61b could indicate their position without interference from the other.

The A.C. power source 30 (FIGURE 212) used to energize the potential field between the casing and ring has a power source such as battery 31, and a siwtch such as 32. This could be a time switch-or could be a proximity switch, which would turn on the source whenever the pipe 20 was removed from the casing, or in many other ways.

I prefer to control the source 30 by signal from the vessel by means of a cable down to a multi-turn coil 74, FIGURE 6, mounted on a non-conducting plate attached to the pipe 20. This can be positioned immediately above the electrodes A, B, C, for example. There is a toroidal transformer 80 surrounding the ring electrode 12. This comprises a cylindrical core 82 and a toroidal winding 84. The leads from this winding go to relay 88. Thus, when an AC. signal is applied from source 78 through switch 76 and leads to the coil 74, an electromagnetic field is set up which encircles the coil 74. Flux that encloses both the coil 74 and the ring 12 will induce current in the ring 12. This will generate current in the winding 84 which will operate the relay 88 to apply power from battery 92 to the power source 94, and thus to apply potential between the casing and ring. So long as the current in 74 is maintained, the relay will hold. Or, if desired, a time-controlled hold can be applied to the relay, to hold it closed for a desired period after the relay is closed by current from transformer 80.

If desired, as shown in FIGURE 8, the current output from the transformer 80 can be connected to a rectifier 106, and battery 108. The battery can supply power to the A.C. source 110. So long as current is supplied to coil 74, the battery 108 will be charging and ready for use. Preferably, the frequency of the current source 78 is much different, and preferably higher, than the signal current applied to the ring 12.

In FIGURE 8, I have shown by dashed lines 114 an alternate connection for the rectifier 106. I show the ring electrode 100 (corresponding to the ring 12). This has a break or'opening 101 with the ends connected to the low turns winding 116 of a step-up transformer 104. The high turns winding 118 is connected by leads 114 to the rectifier 106, etc. Thus, a series step-up transformer can be used with a single turn coil 100, or a multi-turn coil can be used with or without transformer. If a closed coil or ring is used, then the toroidal transformer 80 can be used.

The transmission of signal from the ring 12 to the electrodes A, B, C can be carried on over a large area. Thus, the ring 12, since it is stationary on the sea floor, can be quite large, possibly 50- to 100 feet in diameter. In this case, the spacing of electrodes A, B, C should also be large, although a smaller spacing will still work, but the less resolution. While the preferred diameter of the electrode circle ABC is equal to the radius of the ring 12, this invention will work for smaller'electrode spracings. It is possible also to have a second smaller ring, like 12, FIGURE 9, and concentric with 12, surrounding the casing 10. The power source and transformer 30, 35 can be connected alternately to the smaller and the larger ring by means 39, for example. Or each of the two rings can be excited simultaneously with currents of two different frequencies. The same electrodes A, B, C can be used to detect both signals, which can be separated. by appropriate filters. Thus, a large ring can be used for rough positioning and a small ring for precise positioning.

In the transmission of signal from the ship through coil 74, as shown in FIGURE 6 to the ring 12, it is not practical to carry a very large coil 74 on the riser pipe. Perhaps a practical limit of size would be 10-15 feet, where the ring 12 may be 0-100 feet. In this case, the coil 74 is swept transversely over a large area such that at one time a portion of the coil 74 and ring 12 are close enough so that flux will link both of them. A momentary coupling of flux is all that is needed to switch on the power source 94, FIGURE 6.

Later, when the riser pipe is in final position over the casing, the coil 74 will be concentric with the smaller ring 12 and can be used to transmit power to charge batteries or carry on other operations by suitable coded signals, etc., as is well known in the art.

Of course, any of the embodiments described can be used in various configurations and combinations. Together, they permit signaling from the sea floor to indicate the position of an elongated member, supported from the sea surface, with respect to the casing. Also, by choice of diiferent frequencies of signaling (different frequency source 30) different messages can be transmitted. The various embodiments also provide means to signal and transmit power from the surface to the sea floor installation. Since separate monofrequency signals are sent (in both directions) suitable sharp pass and reject band filters can be used, as is well known in the art, to separate simultaneous signals of different frequencies, and to improve the signal to noise ratio.

I claim:

1. A system for guiding in two dimensions a first end of a movable first cylindrical structure into end-to-end axial alignment with the first end of a fixed second cylindrical structure,. both structures being immersed in a body of sea water, comprising,

(a) a first electrode assembly comprising at least two separate electrodes, said electrode assembly having symmetry with respect to the axis of said second structure,

(b) at least one alternating current means of a first frequency connected between said at least two electrodes, whereby a first current flow is set up in said sea water between said at least two electrodes, said first current flow defining a first series of equipotential surfaces,

(c) a second electrode assembly of at least three electrodes in an array symmetrical about the axis of said first structure, said second electrode assembly positioned near the first end of said first structure in a plane substantially perpendicular to the axis of said first structure, each of said at least three electrodes in said second electrode assembly adapted to take on the potential of the equipotential surface passing through its position, and

((1) means for indicating a quantity related to the potential of each of said electrodes in said second electrode assembly,

whereby when said second electrode assembly is immersed in the current field of said first electrode assembly, and when said first structure is in axial alignment with said second structure, said indications of said quantities related to the potential of each of said at least three electrodes will be equal.

2. The apparatus of claim 1 including means for moving said first structure until a predetermined pattern of potential is detected on said plurality of electrodes of said second electrode assembly.

3. Apparatus as in claim 1 in which said second electrode assembly comprises three electrodes spaced at the verticles of an equilateral triangle.

4. Apparatus as in claim 1 in which said first electrode assembly comprises first linear electrodes parallel. to each other and equally spaced on opposite sides of said second cylindrical structure, and including a second pair of similar linear electrodes similarly placed with respect to said second structure and oriented perpendicular to said first linear electrodes.

5. Apparatus as in claim 4 in which said detecting electrodes comprise at least four electrodes in two pairs, the lines joining the two electrodes of each pair being substantially perpendicular to the directions of the linear electrodes of each pair.

6. Apparatus as is claim 4 in which the alternating current supplied to said first pair of linear electrodes is of said first constant frequency and the current supplied to the second pair of linear electrodes is of a second contrast frequency different from said first frequency.

7. A system for guiding in two dimensions a first structure to be lowered from a vessel floating on a body of sea water for engagement with a second structure on the sea floor, comprising,

(a) a first electrically conducting circular ring of radius r, supported on the sea floor surrounding said second structure and concentric with respect to the axis of said second structure,

(b) a second electrically conducting circular ring of radius R (where R is greater than r) substantially concentric with said first ring, supported on said sea floor,

(c) alternating current means of constant frequency conected between said first and second rings, whereby a current flow is set up in said sea water between said rings, and current flow defining equipotential surfaces,

(d) three equally spaced detecting electrodes mounted on said first structure in a substantially horizontal plane, symmetrically placed with respect to the vertical axis of said first structure and immersed in said sea water, each of said electrodes taking the potential of the equipotential surface passing through its position, and

(e) means for indcating a quantity related to the potential of each of said detecting electrodes,

whereby when the axis of said first structure is aligned with the axis of said second structure, said quantities related to the potential of each of said detecting electrodes will be equal.

8. Apparatus as in claim 7 in which said first ring is a vertical metallic casing in the sediments below the sea floor.

9. Apparatus as in claim 7 in which said means for indicating includes a plurality of potential indcators each connected respectively to one electrode of said second electrode assembly and to a common distant electrode immersed in said sea water.

10. Apparatus as in claim 7 in which said means for indicating includes a plurality of potential indcators each connected respectvely between adjacent pairs of said electrodes.

11. Apparatus as in claim 7 including coil means mounted concentric with said plurality of electrodes on said first structure, alternating current means connected to and circulating a third current in said coil means, and means to utilize the fourth current induced in said second ring electrode by said third current.

12. Apparatus as in claim 11 in which said second circular ring comprises a single turn closed ring of conducting material and including toroidal transformer means inductively coupled to said ring.

13. Apparatus as in claim 11 in which said second circular ring comprises a single turn ring of conducting material, said ring cut and the two ends connected to a step-up transformer.

14. Apparatus as in claim 11 in which said means to utilize said fourth current includes energy storage means.

15. Apparatus as in claim 11 including two second circular rings, both concentric with said first ring, one of diameter substantially equal to said coil means, and the other of much larger diameter.

References Cited UNITED STATES PATENTS 542,732 7/1895 Huskisson 102l 8 1,583,004 5/1926 Osborne 3404 X 2,448,020 8/1948 Darnell 10 218 X 2,514,359 7/ 1950 Allison 10270.2 3,040,658 6/1962 Maltby 10218 3,230,506 1/1966 Hellund 340-4 X 3,264,994 8/1966 Leutwyler 10i219.2 X 3,336,572 8/1967 Paull et a1 3406 FOREIGN PATENTS 510,471 3/1955 Canada.

317,881 l/l92'0 Germany.

578,844 7/ 1946 Great Britain.

RICHARD A. FARLEY, Primary Examiner 

